Memory impairment in ageing is clearly different from Alzheimer's disease. Many papers dealed with the modifications of the different cognitive sections of memory at different stages of Alzheimer's progression: the early involvement of working and episodic memories, those later of semantic and retrograde memories and the lasting saving of implicit memory must be know by clinicians to better understand the target of symptomatic therapy and to differentiate Alzheimer from others degenerative dementias. Above all, these progress authorize an early diagnostic of "possible Alzheimer" at a pre-dementia stage facing to isolated memory complaint. The amnesic profile of others dementias is different and the qualitative approach of testing become essential for the categorization of dementias at early stages with an isolated progressive memory disorder.